U.S. patent application number 13/059209 was filed with the patent office on 2011-06-16 for engine.
This patent application is currently assigned to Yammer Co., Ltd.. Invention is credited to Takao Kawabe, Hidenori Nomura, Tomoo Ogata, Kouji Shimizu, Takeshi Takahashi, Satomi Ukai.
Application Number | 20110138806 13/059209 |
Document ID | / |
Family ID | 41707070 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110138806 |
Kind Code |
A1 |
Takahashi; Takeshi ; et
al. |
June 16, 2011 |
Engine
Abstract
Turbines (21b, 31b) and compressors (21a, 31a), which constitute
superchargers (21, 31), are disposed in series on an exhaust gas
passage (3) and an air intake passage (2), respectively. The
supercharger (31) is equipped with a supercharger rotation sensor
(61), which transmits a detection signal obtained according to the
rotation of the compressor (31a) to a control device, a bypass
passage (4), which bypasses exhaust gas from the upstream side to
the downstream side of the turbine (31b), and a bypass valve (34),
which regulates the flow rate of exhaust gas flowing through the
bypass passage (4). Control device (60) regulates the rotational
speed of the compressors (21a, 31a) in a high-efficiency range by
producing a control signal based on the detection signal from the
supercharger rotation sensor (61), and sending the control signal
to the bypass valve (34).
Inventors: |
Takahashi; Takeshi; (Osaka,
JP) ; Kawabe; Takao; (Osaka, JP) ; Nomura;
Hidenori; (Osaka, JP) ; Ogata; Tomoo; (Osaka,
JP) ; Shimizu; Kouji; (Osaka, JP) ; Ukai;
Satomi; (Osaka, JP) |
Assignee: |
Yammer Co., Ltd.
Osaka-shi, Osaka
JP
|
Family ID: |
41707070 |
Appl. No.: |
13/059209 |
Filed: |
June 11, 2009 |
PCT Filed: |
June 11, 2009 |
PCT NO: |
PCT/JP2009/060669 |
371 Date: |
February 15, 2011 |
Current U.S.
Class: |
60/603 |
Current CPC
Class: |
F02D 41/0007 20130101;
F02B 2039/168 20130101; F02M 26/05 20160201; F02B 2037/122
20130101; Y02T 10/144 20130101; Y02T 10/12 20130101; F02B 37/004
20130101; F02B 37/013 20130101; F02B 37/18 20130101 |
Class at
Publication: |
60/603 |
International
Class: |
F02D 23/02 20060101
F02D023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2008 |
JP |
2008-210947 |
Claims
1. An engine having a plurality of superchargers, each of the
superchargers comprising: a turbine rotatively driven by receiving
exhaust gas flowing in an exhaust passage; and a compressor
rotatively driven by the turbine and pressurizing intake air
flowing in an intake passage, characterized in that the turbines
constituting the superchargers are arranged in the one exhaust
passage in series, the compressors constituting the superchargers
are arranged in the one intake passage in series, at least one of
the superchargers comprises: a supercharger rotation sensor
transmitting a detection signal obtained from rotation of the
compressor constituting the supercharger to a control device; a
bypass passage bypassing the exhaust gas from the upstream side to
the downstream side of the turbine constituting the supercharger;
and a bypass valve limiting the flow rate of the exhaust gas
flowing in the bypass passage, and the control device prepares a
control signal based on the detection signal from the supercharger
rotation sensor and transmits the control signal to the bypass
valve so as to limit the rotational speed of each of the
compressors constituting the superchargers to be within a
high-efficiency range of the supercharger.
2. The engine according to claim 1, further comprising: a fuel
injection nozzle whose fuel injection characteristic can be changed
by a control signal, wherein the control device prepares a control
signal based on the detection signal from the supercharger rotation
sensor and transmits the control signal to the fuel injection
nozzle so as to change the fuel injection characteristic
corresponding to an operating state.
3. The engine according to claim 1, further comprising: a
supercharging pressure sensor detecting the pressure of the intake
air pressurized by the plurality of the superchargers and
transmitting a detection signal to the control device; and an
intake throttle arranged at the upstream side of the supercharging
pressure sensor and limiting the flow rate of the intake air
pressurized by the plurality of the superchargers, wherein the
control device prepares a control signal based on the detection
signals from the supercharging pressure sensor and the supercharger
rotation sensor and transmits the control signal to the intake
throttle so as to limit the pressure of the intake air
corresponding to an operating state.
4. The engine according to claim 3, further comprising: an EGR
passage guiding a part of exhaust gas flowing in the exhaust gas
passage to the intake passage; and an EGR valve limiting the flow
rate of the exhaust gas flowing in the EGR passage, wherein the
control device prepares a control signal based on the detection
signals from the supercharging pressure sensor and the supercharger
rotation sensor and transmits the control signal to the EGR valve
so as to limit the flow rate of the exhaust gas guided to the
intake passage corresponding to the operating state.
Description
TECHNICAL FIELD
[0001] The present invention relates to an engine having a
plurality of superchargers.
BACKGROUND ART
[0002] Conventionally, as an engine having a plurality of
superchargers, an engine having a two-stage supercharging system is
known. In the engine having the two-stage supercharging system, for
example, turbines rotatively driven by receiving exhaust gas are
arranged in one exhaust passage in series, and compressors
pressurizing intake air are arranged in one intake passage in
series. Bypass valves are provided in a bypass passage bypassing
the exhaust gas from the upstream side to the downstream side of
the turbines and a bypass passage bypassing the exhaust gas from
the upstream side to the downstream side of the compressors,
whereby the supercharging pressure can be limited by controlling
the bypass valves (for example, see the Patent Literature 1).
[0003] However, conventionally, in the engine having the
superchargers, only the control is performed in which the
supercharging pressure is limited corresponding to the operating
state of the engine based on detection signals from an intake air
flow rate sensor and a supercharging pressure sensor. Therefore, in
the engine having the two-stage supercharging system, it is
difficult to secure the supercharging pressure corresponding to the
operating state of the engine while limiting the rotational speed
of each of the compressors constituting the superchargers to be
within a high-efficiency range of the supercharger. [0004] Patent
Literature 1: the Japanese Patent Laid Open Gazette 2004-92646
DISCLOSURE OF INVENTION
Problems to Be Solved by the Invention
[0005] The purpose of the present invention is to provide an engine
having a plurality of superchargers in which the supercharging
pressure corresponding to the operating state of the engine can be
secured and rotational speed of each of compressors constituting
the superchargers can be limited to be within a high-efficiency
range of the supercharger, and a control method thereof.
Means for Solving the Problems
[0006] Explanation will be given on means for solving the problems
according to the present invention.
[0007] According to the first aspect of the present invention, an
engine has a plurality of superchargers, each of the superchargers
comprising a turbine rotatively driven by receiving exhaust gas
flowing in an exhaust passage and a compressor rotatively driven by
the turbine and pressurizing intake air flowing in an intake
passage. The turbines constituting the superchargers are arranged
in the one exhaust passage in series. The compressors constituting
the superchargers are arranged in the one intake passage in series.
At least one of the superchargers comprises a supercharger rotation
sensor transmitting a detection signal obtained from rotation of
the compressor constituting the supercharger to a control device, a
bypass passage bypassing the exhaust gas from the upstream side to
the downstream side of the turbine constituting the supercharger,
and a bypass valve limiting the flow rate of the exhaust gas
flowing in the bypass passage. The control device prepares a
control signal based on the detection signal from the supercharger
rotation sensor and transmits the control signal to the bypass
valve so as to limit the rotational speed of each of the
compressors constituting the superchargers to be within a
high-efficiency range of the supercharger.
[0008] According to the second aspect of the present invention, in
the engine of the first mode of the present invention, a fuel
injection nozzle whose fuel injection characteristic can be changed
by a control signal is provided, and the control device prepares a
control signal based on the detection signal from the supercharger
rotation sensor and transmits the control signal to the fuel
injection nozzle so as to change the fuel injection characteristic
corresponding to an operating state.
[0009] According to the third aspect of the present invention, in
the engine of the first mode of the present invention, a
supercharging pressure sensor detecting the pressure of the intake
air pressurized by the plurality of the superchargers and
transmitting a detection signal to the control device, and an
intake throttle arranged at the upstream side of the supercharging
pressure sensor and limiting the flow rate of the intake air
pressurized by the plurality of the superchargers are provided, and
the control device prepares a control signal based on the detection
signals from the supercharging pressure sensor and the supercharger
rotation sensor and transmits the control signal to the intake
throttle so as to limit the pressure of the intake air
corresponding to an operating state.
[0010] According to the fourth aspect of the present invention, in
the engine of the third mode of the present invention, an EGR
passage guiding a part of exhaust gas flowing in the exhaust gas
passage to the intake passage, and an EGR valve limiting the flow
rate of the exhaust gas flowing in the EGR passage are provided,
and the control device prepares a control signal based on the
detection signals from the supercharging pressure sensor and the
supercharger rotation sensor and transmits the control signal to
the EGR valve so as to limit the flow rate of the exhaust gas
guided to the intake passage corresponding to the operating
state.
Effect of the Invention
[0011] The present invention brings the following effects.
[0012] According to claim 1, by controlling the bypass valve based
on the detection signal from the supercharger rotation sensor, the
rotational speed of each of the compressors constituting the
superchargers can be limited to be within the high-efficiency range
of the supercharger. Accordingly, the intake air can be pressurized
to the supercharging pressure corresponding to the operating state
of the engine, whereby the fuel consumption can be reduced.
[0013] According to claim 2, by controlling the fuel injection
nozzle based on the detection signal from the supercharger rotation
sensor, the fuel injection characteristic can be optimized
suitably. Accordingly, the fuel injection corresponding to the
operating state of the engine can be realized, whereby the exhaust
emission can be prevented from being worsened.
[0014] According to claim 3, by controlling the intake throttle
based on the detection signals from the supercharging pressure
sensor and the supercharger rotation sensor, it is not necessary to
provide any bypass passage bypassing from the upstream side to the
downstream side of the compressors constituting the superchargers.
Accordingly, the construction of the engine can be simplified.
[0015] According to claim 4, by controlling the EGR valve based on
the detection signals from the supercharging pressure sensor and
the supercharger rotation sensor, the flow rate of the exhaust gas
guided to the air intake passage can be optimized. Accordingly, the
fuel injection corresponding to the operating state of the engine
can be realized, whereby the exhaust emission can be prevented from
being worsened.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 It is a schematic drawing of entire construction of
an engine having a two-stage supercharging system according to a
first embodiment of the present invention.
[0017] FIG. 2 It is a graph of iso efficiency curves of compressor
performance of superchargers.
[0018] FIG. 3 It is a flow chart of control construction of the
superchargers.
[0019] FIG. 4 It is a schematic drawing of entire construction of
an engine having the two-stage supercharging system according to a
second embodiment of the present invention.
[0020] FIG. 5 It is a flow chart of control construction of
superchargers.
[0021] FIG. 6 It is a schematic drawing of entire construction of
an engine having the two-stage supercharging system according to a
third embodiment of the present invention.
[0022] FIG. 7 It is a flow chart of control construction of an EGR
valve.
DESCRIPTION OF NOTATIONS
[0023] 1 engine body [0024] 2 air intake passage [0025] 3 exhaust
gas passage [0026] 4 bypass passage [0027] 5 EGR passage [0028] 7
bypass passage [0029] 12 intake manifold [0030] 13 exhaust manifold
[0031] 15 fuel injection nozzle [0032] 20 two-stage supercharging
system [0033] 21 low-pressure supercharger [0034] 21a compressor
[0035] 21b turbine [0036] 24 bypass valve [0037] 31 high-pressure
supercharger [0038] 31a compressor [0039] 31b turbine [0040] 33
intercooler [0041] 34 bypass valve [0042] 40 intake throttle [0043]
50 EGR device [0044] 51 EGR valve [0045] 60 control device [0046]
61 supercharger rotation sensor [0047] 62 supercharging pressure
sensor [0048] 100 engine [0049] 200 engine [0050] 300 engine
THE BEST MODE FOR CARRYING OUT THE INVENTION
[0051] Next, explanation will be given on the mode for carrying out
the invention.
[0052] FIG. 1 is a schematic drawing of entire construction of an
engine 100 having a two-stage supercharging system 20 according to
a first embodiment of the present invention. FIG. 2 is a graph of
iso efficiency curves of compressor performance of superchargers 21
and 31. FIG. 3 is a flow chart of control construction of the
superchargers 21 and 31.
[0053] FIG. 4 is a schematic drawing of entire construction of an
engine 200 having the two-stage supercharging system 20 according
to a second embodiment of the present invention. FIG. 5 is a flow
chart of control construction of superchargers 21 and 31.
[0054] FIG. 6 is a schematic drawing of entire construction of an
engine 300 having the two-stage supercharging system 20 according
to a third embodiment of the present invention. FIG. 7 is a flow
chart of control construction of an EGR valve 51.
[0055] Explanation will be given on the construction of the engine
100 which is the first embodiment of the present invention
referring to FIG. 1. The engine 100 is a direct injection type
6-cylindered engine having six combustion chambers, and mainly
includes an engine body 1, an intake manifold 12 to which an air
intake passage 2 is connected, an exhaust manifold 13 to which an
exhaust gas passage 3 is connected, and fuel injection nozzles 15
injecting fuel to the combustion chambers. The fuel injection
nozzles 15 can be controlled their fuel injection timing and the
like by a control signal from a control device 60.
[0056] The engine 100 has the two-stage supercharging system 20.
The two-stage supercharging system 20 has two superchargers, i.e. a
low-pressure supercharger 21 and a high-pressure supercharger
31.
[0057] The air intake passage 2 guides intake air through the
intake manifold 12 to the engine body 1. Along the flow of the
intake air, the air intake passage 2 is provided therein with a
compressor 21a constituting the low-pressure supercharger 21, an
intercooler 23 cooling the intake air pressurized by the compressor
21a, a compressor 31a constituting the high-pressure supercharger
31, an intercooler 33 cooling the intake air pressurized by the
compressor 31a, and an intake throttle 40 limiting flow rate of the
intake air flowing in the air intake passage 2.
[0058] A supercharging pressure sensor 62 is provided in the intake
manifold 12, and detects pressure of the intake air guided to the
engine body 1 and transmits a detection signal to the control
device 60.
[0059] The exhaust gas passage 3 discharges exhaust gas from the
engine body 1 through the exhaust manifold 13. Along the flow of
the exhaust gas, the exhaust gas passage 3 is provided therein with
a turbine 31b constituting the high-pressure supercharger 31 and a
turbine 21b constituting the low-pressure supercharger 21.
[0060] In detail, the low-pressure supercharger 21 is constructed
by the compressor 21a which can pressurize efficiently the intake
air when the engine 100 is at the high-output driving state, and
the turbine 21b rotatively driving the compressor 21a. The
high-pressure supercharger 31 is constructed by the compressor 31a
which can pressurize efficiently the intake air when the engine 100
is at the low-output driving state, and the turbine 31b rotatively
driving the compressor 31a.
[0061] The low-pressure supercharger 21 and the high-pressure
supercharger 31 pressurize the intake air flowing in the air intake
passage 2 by the compressors 21a and 31a. The compressor 21a of the
low-pressure supercharger 21 is arranged at the upstream side of
the air intake passage 2, and the compressor 31a of the
high-pressure supercharger 31 is arranged at the downstream side of
the air intake passage 2.
[0062] In the engine 100 according to this embodiment, a bypass
passage 4 is provided which bypasses the exhaust gas from the
upstream side to the downstream side of the turbine 31b
constituting the high-pressure supercharger 31, and a bypass valve
34 is provided which limits flow rate of the exhaust gas flowing in
the bypass passage 4.
[0063] Furthermore, in the high-pressure supercharger 31, a
supercharger rotation sensor 61 is provided with which a detection
signal obtained by the rotation of the compressor 31a constituting
the high-pressure supercharger 31 can be transmitted to the control
device 60.
[0064] The control device 60 mainly includes a central processing
unit, a storage device and the like. The control device 60 is
connected electrically through an amplifier 65 to the supercharger
rotation sensor 61 provided in the high-pressure supercharger 31,
the supercharging pressure sensor 62 provided in the intake
manifold 12, and engine output set means such as an accelerator
pedal (not shown). The control device 60 prepares a control signal
based on electric signals from these members and outputs the
control signal to the fuel injection nozzles 15 and the like.
[0065] In the control device 60, control maps such as supercharging
map, fuel injection map, intake throttle map and EGR map are stored
so as to drove the engine 100 following requirement of an
operator.
[0066] In each of the control maps such as the supercharging map,
for securing engine rotation speed or torque required by an
operator, optimum control agents previously found by experiment are
stored. Accordingly, the control device 60 calls the control agents
from the control maps and prepares the control signal so as to
control the engine 100 optimally.
[0067] Explanation will be given on the supercharging map in
detail. FIG. 2 is a graph of iso efficiency curves of compressor
performance of the low-pressure supercharger 21 and the
high-pressure supercharger 31. In FIG. 2, the axis of abscissas
indicates flow rate of the intake air flowing to each of the
compressors 21a and 31a, and the axis of ordinates indicates
pressure ratio of the upstream side and the downstream side of each
of the compressors 21a and 31a.
[0068] As shown in FIG. 2, in iso efficiency curves 21map of the
low-pressure supercharger 21, a right end line 21mapR is regarded
as a rotational limit line, and a left end line 21mapL is regarded
as a surge limit line. Each of the rotational limit line and the
surge limit line is a border at which pressurizing efficiency is
reduced widely by instability of flow of the intake air by peeling.
Namely, the low-pressure supercharger 21 can pressurize the intake
air in an area surrounded by the rotational limit line and the
surge limit line, and the center part of the area is regarded as a
high-efficiency range at which the intake air can be pressurized
the most efficiency. Similarly, in the high-pressure supercharger
31, the intake air can be pressurized in an area surrounded by a
rotational limit line and a surge limit line, and the center part
thereof is regarded as a high-efficiency range (see iso efficiency
curves 31map).
[0069] As shown in FIG. 2, the high-efficiency range of the
low-pressure supercharger 21 is formed at the side of high flow
rate and high pressure ratio, and the high-efficiency range of the
high-pressure supercharger 31 is formed at the side of low flow
rate and low pressure ratio. Accordingly, the engine 100 having the
two-stage supercharging system 20 constructed by the superchargers
21 and 31 can obtain the optimum supercharging pressure in the wide
operating area.
[0070] Explanation will be given on the control of the
superchargers in the engine 100 referring to FIG. 3. The control
device 60 calculates a target supercharging pressure Bpatrg, a
target supercharger rotational speed .omega.ctrg and a target
bypass valve opening Ebyp_trg (S110).
[0071] The target supercharging pressure Bpatrg is a supercharging
pressure for optimizing fuel combustion corresponding to the
driving state of the engine 100 and is calculated based on the
supercharging map and the like stored in the control device 60.
[0072] The target supercharger rotational speed ooctrg is a
rotational speed of the compressor 31a for optimizing
pressurization of the intake air in the high-pressure supercharger
31 and is calculated based on the target supercharging pressure
Bpatrg and the supercharging map (see FIG. 3) and the like stored
in the control device 60.
[0073] The target bypass valve opening degree Ebyp_trg is an
opening degree of the bypass valve 34 for setting the rotational
speed of the compressor 31a constituting the high-pressure
supercharger 31 be the target supercharger rotational speed wctrg
and is calculated based on the supercharging map and the like
stored in the control device 60.
[0074] The control device 60 judges whether the absolute value of
the remainder between an actual supercharging pressure Bpa and the
target supercharging pressure Bpatrg is smaller than a
predetermined value .alpha.2 or not as a condition (11) and judges
whether the absolute value of the remainder between an actual
supercharger rotational speed Nta and the target supercharger
rotational speed .omega.ctrg is smaller than a predetermined value
.alpha.3 or not as a condition (12) (S120).
[0075] When the conditions (11) and (12) are satisfied at S120, it
is judged that the two-stage supercharging system 20 performs the
supercharging corresponding to the operating state of the engine
100 and the high-pressure supercharger 31 constituting the
two-stage supercharging system 20 is operated in the
high-efficiency range. In this case, by selecting the compressor
21a operated in the high-efficiency range in the low-pressure
supercharger 21, each of the superchargers 21 and 31 can be
operated in the high-efficiency range.
[0076] The control device 60 can deal with secular degradation of
the engine 100 by revising the target bypass valve opening degree
Ebyp_trg (S130).
[0077] On the other hand, when the conditions (11) and (12) are not
satisfied at S120, it is judged that the two-stage supercharging
system 20 does not perform the supercharging corresponding to the
operating state of the engine 100. Namely, it is judged that the
supercharging pressure is not the optimum value corresponding to
the operating state of the engine 100, or that the high-pressure
supercharger 31 is not operated in the high-efficiency range.
Therefore, the control device 60 limits the opening degree of the
intake throttle 40 so as to satisfy the condition (11) (S140), and
then limits the opening degree of the bypass valve 34 so as to
satisfy the condition (12) (S150).
[0078] Furthermore, when the condition (12) is not satisfied after
repeating the predetermined control at S150 10 times, the control
device 60 judges that abnormality occurs in the supercharger
rotation sensor 61 or the like so as to improve the reliability of
the two-stage supercharging system 20 (S160).
[0079] Accordingly, in the engine 100 according to this embodiment,
the flow rate of the exhaust gas flowing in the bypass passage 4
can be limited based on the supercharger rotational speed Nta of
the high-pressure supercharger 31. Therefore, in the engine 100,
the target supercharging pressure Bpatrg corresponding to the
operating state of the engine 100 can be secured and each of the
low-pressure supercharger 21 and the high-pressure supercharger 31
can be operated in the high-efficiency range, whereby the fuel
consumption can be reduced.
[0080] By preparing the control signal from the rotational speed of
the compressor 31a constituting the high-pressure supercharger 31
and transmitting it to the fuel injection nozzles 15, the control
device 60 can change suitably the fuel injection characteristic
even if the engine 100 is in the transient operating state for
example. Accordingly, the optimum fuel injection corresponding to
the operating state of the engine 100 can be realized so as to
prevent the exhaust emission from being worsened, and the output of
the engine 100 can be controlled accurately.
[0081] Next, explanation will be given on the construction of the
engine 200 which is the second embodiment of the present invention
referring to FIG. 4. The engine 200 according to this embodiment is
similar to the engine 100 according to the first embodiment in the
basic construction, but is provided additionally therein with a
bypass passage 7 which bypasses the exhaust gas from the upstream
side to the downstream side of the turbine 21b constituting the
low-pressure supercharger 21, and a bypass valve 24 which limits
flow rate of the exhaust gas flowing in the bypass passage 7.
[0082] Explanation will be given on the control of the
superchargers in the engine 200 referring to FIG. 5. The control
device 60 calculates the target supercharging pressure Bpatrg, a
target supercharger rotational speed .omega.ctrg_hp of the
high-pressure supercharger 31, a target supercharger rotational
speed .omega.ctrg_lp of the low-pressure supercharger, a target
bypass valve opening Ebyp_trg_hp of the high-pressure supercharger
31, and a target bypass valve opening Ebyp_trg_lp of the
low-pressure supercharger (S210). The calculation of each target
value is similar to that of the first embodiment, and explanation
thereof is omitted.
[0083] The control device 60 judges whether the absolute value of
the remainder between the supercharging pressure Bpa and the target
supercharging pressure Bpatrg is smaller than a predetermined value
.alpha.6 or not (S220). When the condition at S220 is satisfied, it
is judged that the two-stage supercharging system 20 performs the
supercharging corresponding to the operating state of the engine
200.
[0084] On the other hand, when the condition at S220 is not
satisfied, it is judged that the two-stage supercharging system 20
does not perform the supercharging corresponding to the operating
state of the engine 200. Then, the control device 60 limits the
opening degree of one or each of the bypass valve 24 of the
low-pressure supercharger 21 and the bypass valve 34 of the
high-pressure supercharger 31 so as to satisfy the condition at
S220 (S230).
[0085] The control device 60 judges whether the absolute value of
the remainder between an actual high-pressure supercharger
rotational speed Nta_hp and the target supercharger rotational
speed .omega.ctrg_hp of the high-pressure supercharger 31 is
smaller than a predetermined value .alpha.7 or not as a condition
(21) and judges whether the absolute value of the remainder between
an actual low-pressure supercharger rotational speed Nta_lp and the
target supercharger rotational speed .omega.ctrg_lp of the
low-pressure supercharger 21 is smaller than a predetermined value
.alpha.8 or not as a condition (22) (S240).
[0086] When the conditions (21) and (22) at S240 are satisfied, it
is judged that each of the low-pressure supercharger 21 and the
high-pressure supercharger 31 constituting the two-stage
supercharging system 20 are operated in the high-efficiency range.
The control device 60 can deal with secular degradation of the
engine 200 by revising the target bypass valve opening Ebyp_trg_lp
of the low-pressure supercharger 21 and the target bypass valve
opening Ebyp_trg hp of the high-pressure supercharger 31
(S270).
[0087] On the other hand, when the conditions (21) and (22) are not
satisfied at S240, it is judged that the low-pressure supercharger
21 constituting the two-stage supercharging system 20 is not
operated in the high-efficiency range or that the high-pressure
supercharger 31 constituting the two-stage supercharging system 20
is not operated in the high-efficiency range. The control device 60
limits the opening degree of the bypass valve 34 of the
high-pressure supercharger 31 so as to satisfy the condition (21),
and
[0088] limits the opening degree of the bypass valve 24 of the
low-pressure supercharger 21 so as to satisfy the condition (22)
(S250).
[0089] Furthermore, when the conditions (21) and (22) are not
satisfied after repeating the predetermined control at S250 10
times, the control device 60 judges that abnormality occurs in the
supercharger rotation sensor 61 or the like so as to improve the
reliability of the two-stage supercharging system 20 (S260).
[0090] Accordingly, in the engine 200 according to this embodiment,
the flow rate of the exhaust gas flowing in the bypass passage 7
can be limited based on the supercharger rotational speed Nta_lp of
the low-pressure supercharger 21, and the flow rate of the exhaust
gas flowing in the bypass passage 4 can be limited based on the
supercharger rotational speed Nta_hp of the high-pressure
supercharger 31. Therefore, the target supercharging pressure
Bpatrg corresponding to the operating state of the engine 200 can
be secured and each of the low-pressure supercharger 21 and the
high-pressure supercharger 31 can be operated in the
high-efficiency range, whereby the fuel consumption can be
reduced.
[0091] By preparing the control signal from the rotational speed of
one or each of the compressors 21a and 31a constituting the
superchargers 21 and 31 and transmitting it to the fuel injection
nozzles 15, the control device 60 can change suitably the fuel
injection characteristic even if the engine 200 is in the transient
operating state for example. Accordingly, the optimum fuel
injection corresponding to the operating state of the engine 200
can be realized so as to prevent the exhaust emission from being
worsened, and the output of the engine 200 can be controlled
accurately.
[0092] Next, explanation will be given on the construction of the
engine 300 which is the third embodiment of the present invention
referring to FIG. 6. The engine 300 according to this embodiment is
similar to the engine 100 according to the first embodiment in the
basic construction, but is provided additionally therein with an
EGR device 50 which guides a part of the exhaust gas flowing in the
exhaust gas passage 3 to the air intake passage 2.
[0093] The EGR device 50 is constructed by an EGR passage 5 guiding
a part of the exhaust gas flowing in the exhaust gas passage 3 to
the air intake passage 2, an EGR cooler 53 cooling the exhaust gas
flowing in the EGR passage 5, and the EGR valve 51 limiting the
flow rate of the exhaust gas flowing in the EGR passage 5.
[0094] Explanation will be given on EGR control of the engine 300
referring to FIG. 7. The control device 60 can calculate the flow
rate of the intake air from the actual supercharging pressure Bpa
and the supercharger rotational speed Ntahp of the high-pressure
supercharger 31 with an existing formula.
[0095] Firstly, the control device 60 calculates a target EGR rate
EGR_1 and an EGR rate EGRact (S310).
[0096] The target EGR rate EGR_1 optimizes fuel consumption
corresponding to the operating state of the engine 300 and is
calculated with the EGR map and the like stored in the control
device 60.
[0097] The EGR rate EGRact is calculated from an exhaust flow rate
Qair_wot and an EGR flow rate Qair_act. The exhaust flow rate
Qair_wot is the full flow rate of the exhaust gas flowing in the
exhaust gas passage 3 when the EGR valve 51 is fully closed. The
EGR flow rate Qair_act is the flow rate of the exhaust gas guided
to air intake passage 2. The EGR flow rate Qair_act is calculated
by revising the density based on the supercharging pressure Bpa,
the supercharger rotational speed Nta_hp of the high-pressure
supercharger 31, the temperature of the exhaust gas flowing in the
EGR passage 5 and the like.
[0098] The control device 60 judges whether the absolute value of
the remainder between the EGR rate EGRact and the target EGR rate
EGR_1 is smaller than a predetermined value .alpha.5 or not (S320).
When the condition at S320 is satisfied, it is judged that the EGR
device 50 performs the EGR control corresponding to the operating
state of the engine 300.
[0099] On the other hand, when the condition at S320 is not
satisfied, it is judged that the EGR device 50 does not perform the
EGR control corresponding to the operating state of the engine 300.
Then, the control device 60 limits the opening degree of the EGR
valve 51 of the EGR passage 5 so as to satisfy the condition at
S320 (S330).
[0100] Furthermore, when the condition at S320 is not satisfied
after repeating the predetermined control at S330 10 times, the
control device 60 judges that abnormality occurs in the EGR valve
51 or the like so as to improve the reliability of the EGR device
50 (S340).
[0101] Accordingly, in the engine 300 according to this embodiment,
the flow rate of the exhaust gas flowing in the EGR passage 5 can
be limited based on the supercharging pressure Bpa and the
supercharger rotational speed Nta. Therefore, the target EGR rate
EGR_1 corresponding to the operating state of the engine 300 can be
realized, whereby the exhaust emission can be prevented from being
worsened.
INDUSTRIAL APPLICABILITY
[0102] The present invention can be employed in an engine having a
plurality of superchargers.
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